Robot Room Cleaner

class Solution {
    int[][] moves = { { -1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } };
    Set<Pair<Integer, Integer>> seen = new HashSet();
    Robot cleaner;

    public void reverse() {
        cleaner.turnRight();
        cleaner.turnRight();
        cleaner.move();
        cleaner.turnRight();
        cleaner.turnRight();
    }

    public void explore(int x, int y, int dir) {
        seen.add(new Pair(x, y));
        cleaner.clean();
        for (int i = 0; i < 4; ++i) {
            int newDir = (dir + i) % 4;
            int newX = x + moves[newDir][0];
            int newY = y + moves[newDir][1];

            if (!seen.contains(new Pair(newX, newY)) && cleaner.move()) {
                explore(newX, newY, newDir);
                reverse();
            }
            cleaner.turnRight();
        }
    }

    public void cleanRoom(Robot robot) {
        this.cleaner = robot;
        explore(0, 0, 0);
    }
}

For the "Robot Room Cleaner" problem, implement a solution that enables a robotic cleaner to navigate and clean an entire room efficiently. The given Java code uses recursive backtracking to achieve this. Here’s a breakdown of how the solution works:

• Data Structures and Initialization:

  • An array moves that represents the four possible directions the robot can move: up, right, down, and left.
  • A HashSet named seen to keep track of all the cells that have been visited and cleaned.
  • A Robot interface named cleaner which needs methods like turnRight(), move(), and clean().

• Utility Functions:

  • reverse() - This method ensures the robot can backtrack to the previous position. It achieves this by turning around 180 degrees, moving one step forward, and then facing back in the original direction.

• Core Functionality:

  • explore(int x, int y, int dir) - This recursive method is central to the solution. It starts by marking the current position as cleaned. Then, for each of the four possible directions:
    • Calculates the next position based on the current direction.
    • Checks if the new position has not been visited and is accessible.
    • Moves the robot to the new position, cleans it, and recursively explores further from there.
    • On returning from the recursion (post deeper exploration), reverses the robot’s movement to backtrack.
    • Rotates the robot to the next direction to explore.

• Execution Entry Point:

  • cleanRoom(Robot robot) - This method initializes the robot interface and starts the cleaning process from the initial position (0,0) and facing in the initial direction 0.

Ensure that the robot’s interface is correctly implemented to support operations required by this solution. This approach efficiently ensures all reachable parts of the room are cleaned without re-cleaning any area. The recursive depth-first search combined with backtracking provides thorough coverage while the seen set prevents redundant operations.

class Solution:
    def tidyRoom(self, automatedCleaner):
        """
        :type automatedCleaner: Robot
        :rtype: None
        """
        def retreat():
            automatedCleaner.turnRight()
            automatedCleaner.turnRight()
            automatedCleaner.move()
            automatedCleaner.turnRight()
            automatedCleaner.turnRight()

        def explore(cell=(0, 0), direction=0):
            visited.add(cell)
            automatedCleaner.clean()
            for i in range(4):
                new_direction = (direction + i) % 4
                new_position = (cell[0] + movement[new_direction][0],
                                cell[1] + movement[new_direction][1])

                if new_position not in visited and automatedCleaner.move():
                    explore(new_position, new_direction)
                    retreat()
                automatedCleaner.turnRight()

        movement = [(-1, 0), (0, 1), (1, 0), (0, -1)]
        visited = set()
        explore()

The "Robot Room Cleaner" solution in Python involves a robot that cleans a room autonomously by navigating through all accessible areas. Here's a concise summary of how the implementation works using Python classes and functions:

• A Solution class contains the method tidyRoom that receives an instance of Robot as its parameter.
• The inner function retreat() handles the robot's movement to backtrack. It involves turning the robot around (180 degrees) by executing two right turns, moving one step backward, and then aligning back to the original facing direction with two additional right turns.
• The explore function is a recursive method that takes two parameters: cell, indicating the robot's current position with a default starting position of (0, 0), and direction, representing the current facing direction with a default direction of 0.
• In the explore function:
  • The robot's current cell is added to the visited set.
  • The clean() method of the robot is called to clean the current cell.
  • The robot attempts to explore in all four directions (represented by the indices 0-3). The direction is dynamically adjusted based on the robot's current direction plus the incremental directions from a loop.
  • A new position is calculated based on the current direction. If this new position has not been visited and the robot can move there (automatedCleaner.move() returns True), the explore function is recursively called.
  • After exploring the new position, the robot then calls the retreat() function to go back to the previous cell before continuing to turn and explore other directions.
• The movement list defines the change in coordinates corresponding to each direction (up, right, down, left).
• The visited set keeps track of all cells that the robot has cleaned to prevent redundant cleaning and movement.

Effectively implement this recursive backtracking approach to ensure the robot cleans the entire accessible area without repeating any locations. By combining the recursive exploration of areas and manual management of robot orientation and position, this solution ensures thorough cleaning of the room.